1. Technical Field
The present invention relates to a technique for detecting an object that has emerged within a monitor region, on the basis of an image obtained by photographing the monitor region.
2. Related Art
There have been conventional techniques for monitoring the presence of an intruding object (including an intruder) that has invaded a monitor region. Specifically, in these techniques, an intrusion detection device analyzes input images based on a video signal from a camera photographing the monitor region, and detects an object that has emerged within the monitor region.
Conventional intrusion detection devices will be described.
One exemplary intrusion detection device is implemented using a computer that includes: an image input I/F that converts an analog video signal obtained from a camera into a digital video signal (A/D conversion) and provides input images each of which is expressed by a luminance signal having a predetermined tone number; an image memory that is used to make a calculation between the images and store these; a CPU (Central Processing Unit) that performs an image analyzing process; an input and output I/F that receives command signals and the like from the outside and transmits alarm signals and the like to the outside; a working memory that serves as a working region for the CPU; a program memory that stores a program for the above image analyzing process; an image output I/F that converts the digital images stored in the image memory into an analog video signal (D/A conversion) and outputs it to the outside (e.g., monitor screen); and a data bus through which the above functional units transfer data.
First, the intrusion detection device creates a background image to be used for intrusion detection. This background image is created with a plurality of input images that have been obtained from the camera through the image input I/F at preset frame intervals. Specifically, the intrusion detection device creates an image in which no object (intruding object) targeted for detection is present, by calculating the weighted average of a plurality of temporally differing input images.
After the creation of the background image, the intrusion detection device repeatedly performs both an object detecting process and a video displaying process, which will be described below, every time capturing the video signal (input image) from the camera. In addition, when detecting an intruding object (including an intruder), the intrusion detection device performs an alarm process.
In the object detecting process, the intrusion detection device calculates the difference between the created background image and a newly captured input image, creating a difference image (input image−background image). Then, the intrusion detection device creates a binary image by binarizing the difference image with a predetermined binary threshold, and creates a noise-removed image by removing noises (cluster of multiple pixels) contained in the binary image. Following this, the intrusion detection device regards the clusters of pixels left on the noise-removed image as objects, labels each object (cluster), and calculates the width, height and area of each object. Next, the intrusion detection device determines whether each labeled object is a person (intruder) or not by identifying the type of each object on the basis of its size, staying time, moving distance, and the like. If the object is determined to be an intruder, the intrusion detection device performs an alarm process in which an external apparatus outputs an alarm, for example, by lighting Patlite (registered trademark) lamp, sounding a buzzer, or telling a server. In this process, the intrusion detection device updates the background image every time capturing an input image from the camera, in order to follow a temporal, continuous state change in the video.
In the video displaying process, the intrusion detection device outputs the input images captured from the camera to, for example, a monitor that an observer is watching, through the image output I/F, and then displays these input images on the monitor. In addition, if an intruder is present, the intrusion detection device superimposes letters “intruder detected,” a marker indicating the detected location, and the like onto the input images, and then outputs these images (intruder-information-added images) to the monitor.
Various inventions regarding object detection have been proposed so far. For example, JP 2009-117956 A discloses the invention of an object detection method that considers a case of being applied to integrated security systems and traffic analyses under complex disturbance, for example, in which brightness constantly or temporarily changes, a leaf or water surface moves, or snow or rain causes attenuation.